067 
fxak68 pafc 202234 
afdafc 


Area forecast discussion 
southcentral and southwest Alaska 
135 PM akst Thursday Nov 20 2008 


Analysis and upper levels...Gulf/NE Pacific low complex has now 
merged into a single center over the southern Gulf. Remnants of 
the occluded front from this low are pushing northwest across 
western portions of southcentral. Radar/satellite imagery show a 
band of snow from Kodiak Island northward to the Kenai Peninsula 
and the Anchorage/mat-su region. Snow is generally light...but radar 
echoes indicate greater intensity snow on the western Kenai 
Peninsula. Moisture on the east side of the trough/upper low is 
streaming northwestward along the far eastern Gulf and into the 
Copper Basin...bringing some light snow to eastern portions of the 
basin. Winds across the Gulf and southcentral are slowly beginning 
to diminish as the low drifts southeastward. 


An upper level low is dropping down into southwest Alaska this 
morning...bringing lots of Arctic air with it. Cold advection 
induced winds area affecting some locations...but a deep surface 
based inversion across interior southwest Alaska is keeping the 
stronger winds aloft from mixing down to the surface. 


A large cold core low has moved out of eastern Asia into the Sea 
of Okhotsk. A strong jet with estimated maximum speed around 180kt 
extends from Japan northeastward to the western Aleutians. This 
jet is driving a surface front eastward across the Bering and 
Aleutians...and gradually eroding the ridge over the eastern Bering. 


A surface low has formed along the front in the left exit region 
of the upper jet and location of maximum upper level diffluence. 
This low is tracking across the western Aleutians into the Bering 
Sea and will continue to deepen under such favorable conditions. 


Model discussion...models initialized well with synoptic 
positions...but solutions quickly diverge...especially with the 
Bering Sea system. Continue to prefer the GFS in the Gulf because 
it has performed better than the NAM the past couple days. Out 
west...like the general idea of multiple triple point development 
as the strong upper jet drives eastward along the Aleutians Friday. 
Model solutions are grouped in the same general area. 
However...beyond 48 hours solutions diverge with evolution of 
these triple point lows as well as entrance of next major system 
out west. Thus...changes to forecast will be confined to the first 
48 to 60 hours. 


Short term forecast... 


Southcentral Alaska...winds will diminish tonight across the region 
as the Gulf low tracks eastward. Most of the precipitation will 
also end as the low moves away. However...the trough dropping down 
through southwest Alaska will swing northeastward and moves across 
southcentral late tonight through Friday night. It looks like there 
will be enough left over moisture in place to generate a local areas 
of snow...especially along the mountains. If accumulation occurs it 
will be very minor. A triple point low associated with the Bering 
Sea system will move into the Gulf Friday night and northward toward 
southcentral Saturday. Although the details of the track of this low 
are in question...it looks like a good chance of snow for most areas. 
This system won't hang around long as the pattern becomes very 
progressive. So it will likely exit Sunday as a new system comes 
into the picture. 


Southwest Alaska...cold advection winds will continue this evening 
and then diminish overnight into Friday as the upper trough begins 
to swing northeastward...ending most of the cold advection. The 
Bering Sea systems will pass mainly to the south...impacting only 
southern portions of Bristol Bay as well as the Alaska Peninsula. 
Areas to the north will remain cold and dry through at least 
Saturday. Another Bering storm system will approach southwest 
Alaska Sunday. With large model disagreements details are not 
clear at this time. 


Bering Sea Aleutians...storm force winds will develop along the 
Aleutians and Bering Sea tonight as a low deepens over the central 
Bering. Triple point lows will quickly develop to the east on Friday 
as the jet moves eastward. Thus the parent low will quickly weaken 
Friday and Friday night. The pattern will continue to progress 
through the weekend with another strong storm moving to the Aleutians 
Saturday and likely replaying a similar scenario with triple point 
development in a very dynamic environment. 


Long term forecast...a very progressive hemispheric pattern with a 
strong sub-tropical jet will lead to a very stormy extended period 
with rapidly changing conditions across the forecast area. This will 
make it very difficult to forecast the details of these storms very 
far out in time. 


Aer/alu...watch/warning summary 
public...none. 
Marine...Storm Warning...179 185. 
Gale Warning...130 132 150 155 165 170 171 172 175 176 180. 
Heavy freezing spray...160 180 185. 
Fire weather...none. 


Seb Nov 08 

National Weather Service Glossary of Abbreviations

Non-Expanded Version (with abbreviations)